Spray-applied cellulose insulation and method

ABSTRACT

A spray-on cellulose insulation and method of application is described herein. The insulation comprises cellulose and an adhesive having gelling properties during application, preferably polyvinyl alcohol. The cellulose includes an additive that triggers gelling of the adhesive upon application to the cellulose. The cellulose preferably also includes a crosslinker for the adhesive. The additive and the crosslinker may be the same, which means the crosslinker is sufficiently alkaline to also trigger the gelling of the adhesive upon application of the adhesive to the cellulose. The gelling of the adhesive allows a reduction in the level of moisture added to the cellulose fibres to below 20%, resulting in an insulation with rapid drying times, reduced risk for fungal growth, lower applied densities and a total moisture content below 30% on an oven dry basis.

FIELD OF THE INVENTION

The present invention relates generally to building insulation. More particularly, the present invention relates to spray-applied fibre based insulation, most specifically spray-applied cellulose fibre insulation.

BACKGROUND OF THE INVENTION

Sprayed cellulose building insulation is generally made from recycled paper or paperboard stock modified with chemical additives. It can be applied to open surfaces or cavities that will be enclosed later. Cellulose insulation is an alternative to commonly used fibreglass insulation in the form of batts or loose fill. Because of the loose nature of the insulation material, sprayed cellulose fibre insulation can be applied to a wide range of areas, including attics, walls, floors or any other voids or hard-to-reach crevices where batt insulation is not easily applied. It forms a uniform covering throughout the cavity and forms a superior air seal around electrical boxes, wiring, pipes and framing members. To reduce ignition and combustion danger, the cellulose material is generally treated with fire retardants, for example boric acid. Antifungal agents are also generally added to the cellulose material to prevent the growth of potential pathogens such as mould.

Cellulose building insulation has been lauded for its energy efficiency and environmental friendliness. The manufacture of cellulose insulation uses less energy (up to 59 times less) and releases fewer greenhouse gases into the atmosphere than that of mineral fibre insulation, which requires vast amounts of heat derived from natural gas combustion. In addition to its environmental conservation benefits, spray applied cellulose has been shown to possess R-values superior to other loose-fill insulation, and to reduce air infiltration, which lowers heating energy costs.

Despite documented and well-established benefits, there are a number of challenges to the effective application and use of cellulose insulation in the field. Blown cellulose fibre material does not have sufficient integrity to be applied into wall cavities “dry”, which means without added moisture. To prevent the blown-in “dry” material from falling out of the wall cavity, some type of retaining structure such as netting must be used which maintains the insulation in place. If the insulation is to be permanently applied to a surface or in a cavity without such a retaining structure, sufficient water or water and adhesive mixture must be added to achieve a bonding of the fibres to one another and to the surface to which they are applied. Furthermore, to prevent settlement of the sprayed insulation, the fibres are bonded to one another as well as to the substrate to which they are applied. This increases the moisture content of the insulation upon application.

Typically, cellulose inherently has a moisture content of 5 to 10%, but further moisture is generally added during spray application to bond the cellulose fibres, in particular for wall applications. It is the use of this added moisture, which creates additional challenges. As insulation loses R-value when wet (hence, reducing thermal performance), wet-applied cellulose insulation cannot function at an optimal level until adequately dry. Thus, wet insulation needs to be dried in-situ before closing of the wall cavity, which delays contractors and building completion. Depending on environmental factors, this can lead to costly construction delays, particularly in humid climates, since the level of humidity can greatly affect drying times. Further, there is a perception that cellulose insulation applied with excessive moisture will lead to problems in terms of rot and mould growth. Although this is not true for the cellulose fibres which are generally treated against the growth of such pathogens, surrounding untreated building materials may already include mould and rot spores which may grow in the presence of sufficient excess moisture.

The US Forest Products Laboratory has determined through numerous tests that the growth of wood rotting fungi is retarded at an average moisture content of 25-30% and is completely stopped at 20% based on the oven dry weight condition. Thus, there are concerns that if the insulation remains above a moisture content of 30% for extended periods of time there is a potential for mould growth in adjacent untreated building materials and, thus, potential health problems. Consequently, a need exists for a spray applied cellulose insulation of the lowest possible moisture level.

A high moisture content of the applied cellulose insulation not only creates challenges with respect to the growth of pathogens and reduced R-value, but also increased density. Since increased densities result in increased material requirements, a need exists for a spray applied cellulose insulation of the lowest possible density in order to keep material costs competitive with other insulation products.

Devices for spray applying insulation have been well documented. Devices are disclosed in U.S. Pat. No. 1,718,507 (Wenzel et al.), U.S. Pat. No. 1,978,125 (Bennett), U.S. Pat. No. 3,606,154 (Tufts), U.S. Pat. No. 3,861,599 (Waggoner), U.S. Pat. No. 3,957,209 (Thomson) and U.S. Pat. No. 4,236,654 (Mello).

Spray-on cellulose insulation has been described in U.S. Pat. No. 4,360,440 (Nov. 23, 1982), issued to Boyer et al., which discloses a cellulose insulation containing 50% water, 33% cellulose fibres and 17% adhesive resin, the adhesive comprising an adhesive mixture of 40% sodium silicate (@ 41% solids) and 60% acrylic resin (@46% solids). Assuming an inherent moisture content of the cellulose fibres of 10%, the resulting cellulose insulation has a moisture content on an oven dry weight basis of 167%.

In this context, oven dry refers to the oven dry testing method known in the art wherein for achievement of the oven dry condition the drying conditions are selected to completely drive out all moisture in the material and wherein the moisture content of the material is expressed in percent of the total weight of the material relative to the weight of the material in the oven dried condition.

U.S. Pat. No. 5,684,068 (Nov. 4, 1997), issued to Boyer et al. discloses insulation compositions including polyvinyl alcohol (PVOH) cooked without an acidic medium and cellulose fibres combined with an acidic medium (boric acid) for spray-on insulation. The boric acid is admixed with the cellulose fibres in a dry or dissolved condition and not admixed with the PVOH during cooking. The treated cellulose fibres disclosed for use in spray-on applications in Table 1 have a moisture content of 10 to 15%, on an oven dry basis. Samples were prepared by applying 0.23 gallons (0.87 L) of adhesive mixture to 1 lb. (0.45 kg.) of cellulose fibres. Mixtures were produced using either a 5:1 or 4:1 ratio of water to resin mixture. The oven dry moisture content of the resulting insulation would be in excess of 125%.

U.S. Pat. No. 5,853,802 (Dec. 29, 1998), issued to Boyer et al. (continuation-in-part of U.S. Pat. No. 5,684,068), discloses a method for treating cellulose fibres with solid boric acid at a level of 15-30% by weight, or a mixture of 10-25% solid boric acid with 0-12% aqueous boric acid. The disclosed cellulose insulation for application into walls also has a moisture content on an oven dry weight basis of in excess of 125%.

U.S. Pat. No. 6,251,476 (Jun. 26, 2001), also issued to Boyer et al., discloses a method for applying cellulose insulation in walls, wherein the PVOH adhesive is “cooked” with or without the presence of an acidic medium, prior to addition to the cellulose fibres. A PVOH adhesive mixture is added to the fibres at a level of about 0.05 to about 0.3 gallons (0.19-1.13 L) of adhesive per pound (0.45 kg) of fibres. Further, the ratio by volume of water to adhesive resin is between 3:1 to 15:1, resulting in an insulation density of 1.5 to 6 lb./ft³. (24.0-96.2 kg/m³). On the basis that the oven dry moisture content of the cellulose is 10% (inherent moisture), the adhesive resin used in the adhesive mixture contains 30% solids (i.e. 70% water) and the density of the adhesive mixture is 8.35 lb/ft³, the minimum oven dry moisture content for this method (3:1 adhesive added at a rate of 0.05 gal per pound of fibre) would be 52%. The maximum oven dry moisture content (15:1 adhesive added at a rate of 0.3 gal per pound of fibre) for this method would be 270%.

As is apparent, the prior art discussed above all results in applied products with a density in excess of 24.0 kg/m³ (1.5 lb/ft³) and a moisture content on an oven dry weight basis which greatly exceeds the minimum moisture levels required for preventing fungal growth. Furthermore, tests with commercially available cellulose systems show that simply reducing the amount of added moisture and/or aqueous adhesive to achieve a total moisture level in the finished insulation below 30% is not an option, since this results in an unacceptable final product. Under the reduced moisture conditions, prior art cellulose insulations exhibit insufficient integrity to prevent unacceptable settling over time and insufficient wet strength to prevent excessive amounts of material falling out of the wall cavity during application. Thus, an improved spray-applied cellulose insulation system is desired which permits the achievement of the desired moisture content after application for limiting fungal growth, can be economically applied at a lower density to a surface or cavity and has sufficient integrity to prevent undesirable settling and has sufficient wet strength.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at least one disadvantage of previous spray-applied cellulose insulation types.

The inventors of the present cellulose insulation and application method have surprisingly found that a cellulose insulation with acceptable integrity and wet strength for application to upstanding surfaces such as walls and having a moisture content below 30% on an oven dry weight basis can be achieved. The inventors have further found that such a cellulose insulation can be reliably applied at this moisture content to upstanding surfaces, such as walls, without the previously expected settling and integrity problems by using an adhesive system, which provides a gelling of the adhesive upon application thereof onto the cellulose. The inventors have also surprisingly found that with the cellulose insulation of the invention an insulation density below 24.0 kg/m³ (1.5 lb/ft³) can be achieved. Although the potential for gelling of certain adhesives during storage was previously observed as disclosed in the prior art (see U.S. Pat. No. 5,684,068), this effect was considered undesirable and was prevented in the prior art insulation application methods by the addition of an acidic medium to the cellulose fibres. The inventors of the present application have now discovered that, contrary to the teachings of the prior art, a gelling of the adhesive can be used to improve the integrity and wet strength of the cellulose insulation when the gelling is triggered upon application of the adhesive to the cellulose during spray application of the insulation to an upstanding surface.

According to one object of the invention there is provided a spray-on cellulose insulation including cellulose fibres and an aqueous adhesive resin for binding the fibres at application, wherein the moisture content of the cellulose fibre insulation is less than 30%, more preferably between about 15% and 25% and most preferably below 20% as measured on an oven dry weight basis.

According to another object of the present invention there is provided a spray-on cellulose insulation including cellulose fibres for spray-on application and an aqueous adhesive resin for bonding the fibres at application, the adhesive resin being capable of forming a wet gel prior to drying and the cellulose fibres being treated prior to spray-on application with an additive which triggers gelling of the adhesive resin upon application of the adhesive to the fibres.

In yet another object of the invention, the cellulose fibres are further treated with a cross-linking agent.

In still another object of the invention there is provided a cellulose insulation having a density between 16.0-24.0 kg/m³ (1.0-1.5 lb/ft³), preferably 20.0-24.0 kg/m³ (1.25-1.5 lb/ft³).

It is a further object of the present invention to provide a method for insulating an upstanding surface by application of the spray-applied cellulose insulation of the invention, the method including the steps of selecting an additive/aqueous adhesive resin combination resulting in a gelling of the adhesive upon admixture of the adhesive with the additive, treating cellulose fibres with the additive, blowing the treated cellulose fibres onto the upstanding surface, and spraying the adhesive resin onto the cellulose fibres prior to the fibres impinging on the upstanding surface, to trigger gelling of the adhesive resin upon application of the cellulose fibres to the surface and prior to setting of the adhesive resin.

In accordance with the invention, the aqueous adhesive resin can be selected among any of the known resins capable of generating a wet gel under conditions compatible with spray application of cellulose insulation. The preferred aqueous adhesive resin in accordance with the invention is polyvinyl alcohol or any mixture thereof with other adhesive resins, for example polyvinyl acetate, which do not interfere with the gelling of the adhesive upon application thereof to the treated cellulose fibres.

According to yet a further object of the invention, the additive and the cross-linker are either different compounds, or a single compound capable of triggering gelling of the adhesive as well as functioning as a cross-linker for the adhesive.

In a further aspect, the invention provides a cellulose insulation product including cellulose fibres for spray application to an upstanding surface, the cellulose fibres having been treated with an additive for triggering gelling of an aqueous adhesive resin upon admixture therewith, and instructions for use of the cellulose fibres in a spray-applied application in combination with the aqueous adhesive resin to achieve a cellulose insulation having a total moisture content of less than 30% on an oven dry weight basis.

In a preferred embodiment, the cellulose insulation product further includes an amount of the aqueous adhesive resin separate from the cellulose fibres to prevent contact thereof prior to use of the adhesive according to the instructions.

In still another aspect, the invention provides an adhesive system for use in spray-applied cellulose fibre insulation, comprising an aqueous adhesive resin for application to the cellulose fibres during spray-application of the insulation, the adhesive resin being capable of generating a wet gel, and an additive for triggering gelling of the adhesive resin upon admixture therewith. The adhesive preferably includes polyvinyl alcohol (PVOH) or a mixture thereof with polyvinyl acetate (PVA). The ratio is preferably from 1 to 10 parts PVA to 1 part PVOH, more preferably from 1 to 5 parts PVA to 1 part PVOH and most preferably 3 parts PVA to 1 part PVOH. The additive for use in combination with the PVOH containing adhesive must raise the pH of the adhesive to a value above 7.0, preferably above 8.0, most preferably borates selected from the group of ammonium pentaborate, ammonium biborate, sodium pentaborate.

Preferred additives for use with PVOH containing adhesives are pH alkaline borates such as ammonium pentaborate, ammonium biborate and sodium pentaborate, which simultaneously function as additives triggering gelling of the adhesive and as crosslinkers during setting of the adhesive.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying examples.

DETAILED DESCRIPTION

Generally, the present invention provides a spray-on cellulose insulation with improved integrity and wet strength. Specifically, the invention provides a cellulose fibre insulation comprising treated cellulose fibres and an adhesive resin for binding the fibres at application, wherein the total moisture content of the cellulose fibre insulation on an oven dry weight basis is less than 30%.

The overall water added to the cellulose fibres of the present invention is 5-24% (w/w), optionally 10-20% (w/w). The nominal added moisture is derived from the water, mixed with the adhesive resin. At a mixing ratio of 3 parts water to 1 part adhesive resin the nominal added water is 4-18%. The total moisture content of the applied insulation on an oven dry weight basis is less than 30%. In this context, applied insulation refers to the cellulose insulation directly after spraying the cellulose and adhesive onto an upstanding surface such as a wall surface. This takes into account that cellulose has an inherent moisture content of 5-10% on an oven dry weight basis. In the following, the terms “wall surface” or “wall cavity” are intended to encompass any upstanding surface or cavity to be insulated.

Advantageously, the reduced added moisture significantly reduces and potentially obviates drying time, thus allowing construction crews to complete dry wall and related structural tasks with little or no delay after application of the insulation. It is a further advantage of the present invention to provide a reduced-moisture cellulose fibre insulation which nevertheless has sufficient wet strength to remain in a wall cavity during and after application. By keeping the total moisture content on an oven dry weight basis below 30%, fungal growth in raw wood materials surrounding the cellulose insulation is retarded and by keeping the total moisture below 25%, fungal growth is virtually eliminated. It is still a further advantage of the present invention to provide a cellulose fibre insulation in which the thermal degradation period is reduced via a reduction in the amount of time required for the insulation to dry down to ambient conditions. Advantageously, reducing the total added water does not compromise the integrity of the insulation as long as cellulose insulation is applied with an adhesive/additive combination which provides a gelling of the adhesive upon mixture with the additive. It is this gelling of the adhesive upon application, which is believed to provide additional wet strength to the insulation upon application, thereby allowing a reduction in added moisture previously believed impossible. Adhesives/additive combinations applicable for use in the present application include any known aqueous adhesives which are capable of generating a wet gel and their respective gel triggering compounds (additives).

Prior to spray application, the cellulose fibres are treated with the additive by either admixing the additive in a granular or liquid form with the fibres, or by pounding or spraying it into the cellulose fibres in a fibre mill. When the adhesive used is or contains PVOH, the additive is an alkaline compound used in a sufficient amount to trigger gelling of the PVOH upon admixture therewith. Additives preferred for use in combination with PVOH are alkaline additives having a pH above 7.0, most preferably above 8.0. The alkaline additive is used in an amount sufficient to trigger gelling of the adhesive upon application of the adhesive to the treated cellulose fibres. The cellulose fibres can also be treated for use with PVOH based adhesive with a crosslinker. Most preferably, the cellulose fibres are treated with a crosslinker which is sufficiently alkaline in solution to triggers gelling of the adhesive upon contact with the treated fibres. Examples are ammonium pentaborate, ammonium biborate or the alkaline earth metal borates. Crosslinkers which are not or only slightly alkaline can also be used when combined with a sufficient amount of an alkaline additive to render the mixture alkaline in solution. Mixtures of acidic crosslinkers with alkaline additives in sufficient amount to render the mixture alkaline in solution are also possible. The alkaline compound for use in admixture with the crosslinker is selected to be storage stable and to be compatible with the cellulose fibres and the adhesive to be used. An exemplary acidic mixture of crosslinker and alkaline compound is boric acid and sodium hydroxide in which the sodium hydroxide is added to the resulting mixture in sufficient quantity to achieve alkalinity. Other alkaline compounds which may be used are alkali earth metal oxides, bicarbonates; carbonates or organic base.

The cellulose fibres are preferably admixed with a sufficient amount of fire retardant to render the insulation compliant with applicable building regulations, especially regulations regarding flammability and smoldering resistance. A fire retardant typically used in the prior art is boric acid. The cellulose fibres are treated prior to being added to a hopper used in applying the treated cellulose to the surface being insulated.

Gelling testing was performed with exemplary combinations of adhesive (PVOH containing) and alkaline additive and the results are shown in Table 1. TABLE 1 Experiment Adhesive Cellulose Additive Result Control 4 parts 1 part Boric Acid No gelling 4% polyvinyl alcohol 1 4 parts 1 part Boric Acid + Gelling 4% polyvinyl Sodium hydroxide to alcohol raise pH to >7.0 2 4 parts 1 part Boric Acid + Gelling 4% polyvinyl Potassium hydroxide to alcohol raise pH to >7.0 3 4 parts 1 part 4% ammonium Gelling 4% polyvinyl pentaborate (pH 7.8) alcohol 4 4 parts 1 part 4% ammonium Gelling 4% polyvinyl biborate (pH 8.9) alcohol 5 4 parts 1 part 4% sodium Gelling 4% polyvinyl pentaborate (pH 9.0) alcohol 6 4 parts 1 part 4% sodium Gelling 4% polyvinyl bicarbonate to raise alcohol pH to >7.0 7 4 parts 1 part 4% boric acid + Gelling 4% polyvinyl small amount of 99% alcohol 2-aminoethanol 8 4 parts 1 part 4% boric acid + Gelling 4% polyvinyl small amount of 4N alcohol ammonium hydroxide

According to the present invention, an adhesive is added to the cellulose fibres upon spray-application. In one embodiment, an aqueous adhesive resin comprising 3 parts acetate and 1 part PVOH is used, although any suitable aqueous adhesive capable of gelling may be used. Typically, the adhesive concentration is 1-15% (w/w), preferably 5-10%, with a final dry adhesive content of 0.25-3% (w/w), optionally 1-2% (w/w). The adhesive is added to the cellulose fibres at the moment of spray application to the surface to be insulated. No pre-treatment of the cellulose fibres with adhesive or “cooking” is required.

In a preferred embodiment of the invention, an alkaline crosslinker is used which functions as the alkaline additive, namely sodium pentaborate. It is added to the cellulose fibres in an amount of 5-15% (w/w), optionally 8-10% (w/w).

The adhesive on application exhibits a “gelling” effect, instantly binding the cellulose fibres to the surface providing a stronger wet bond than if gelling is not forced. This effect is not experienced with other commercially available adhesive and cross-linking mixtures, such as acrylic-latex. Since the gel-triggering additive is applied to the cellulose, the gelling effect does not hinder the application of the insulation because it only occurs after the cellulose has been sprayed through a spray nozzle and adhesive applied thereto. Thus, there exists little concern for clogging within the spray nozzle and hose.

To achieve a total moisture content on an oven dry weight basis below the desired 30% in a cellulose insulation having an initial moisture content between 5-10%, the amount of aqueous adhesive added to the cellulose fibres should be between 0.26 and 0.20 L adhesive/kg of cellulose fibres respectively (0.3 to 0.2 gallons adhesive/lb of cellulose fibres). Ideally, the final concentration of stock adhesive mixture prior to insulation application is about 7% solids. At this concentration the amount of dry adhesive solids added to the finished product is between 1.5 to 2.0%. The adhesive mixture is made by mixing 3 parts water to 1 part adhesive resin. At this ratio the nominal amount of water added to the insulation is 0.20 to 0.15 L (0.05 to 0.04 gal) and the nominal amount of adhesive resin added to the insulation is 0.06 to 0.05 L (0.25 to 0.19 gal). The amount of added water as tested (see Example 1) was about 10%, resulting in a total moisture content on an oven dry weight basis of 18%.

Because of the reduced added water and the resulting lowering of the insulation density, the amount of material required to insulate an area is significantly lower than with competing spray-on cellulose insulation systems. Typically, the density of cellulose fibre insulation provided by the present invention is less than 24.0 kg/m³ (1.5 lb./ft³) compared to 36.1 kg/m³ (2.25 lb./ft³) in current commercially available technology. Advantageously, when the cost per weight is factored into the equation, the material cost of using the insulation of the present invention is significantly lower than the cost of competing systems. Even further reductions in cost can be achieved when the insulation is applied by an individual with sufficient skill.

The present invention further provides a method for insulating a surface comprising the steps of treating cellulose fibres with a crosslinker and applying the cellulose fibres to a surface by spray mixing the treated cellulose fibres with an aqueous adhesive resin mixture to form a cellulose fibre insulation, wherein the cellulose fibre insulation upon application has a total moisture content on a oven dry weight basis of less than 30%. The cellulose fibre insulation is prepared as described above. The cellulose fibre insulation can be applied to any surface, not limited to walls, ceilings, floors and crevices.

The method comprises blowing treated cellulose fibres under pressure through a first hose and spray nozzle and simultaneously applying through a second hose and under pressure an aqueous adhesive resin mixture as the treated cellulose fibres exit the spray nozzle, which adhesive resin will react with the additive in the cellulose. The aqueous adhesive resin mixture will gel upon contact with the treated cellulose, due to the gelling triggering additive included in the cellulose.

The additive is selected to trigger a gelling of the adhesive upon application of the adhesive to the fibres.

For on-site insulation applications, commercially available cellulose spray application equipment is preferably used (e.g. Krendl, Intec Spray Equipment Manufacturers). The cellulose fibres are prepared by an insulation machine and blown under pressure through an insulation delivery hose to an application nozzle. Adhesive mixture is pumped through an adhesive delivery hose to spray tips adjacent the insulation application nozzle. The spray nozzle includes multiple spray tips. Treated cellulose and adhesive are simultaneously ejected from the application and spray nozzles respectively to admix prior to impacting on the application surface. Bales of cellulose fibre insulation, treated with the additive, are loaded into a hopper of the insulation machine. The feed rate and air pressure of the machine are adjusted to deliver the insulation at the application nozzle at a predetermined rate and in an even and consistent fashion. An adhesive delivery pump is connected to or placed in a vessel of premixed aqueous adhesive resin for delivery of the adhesive under pressure to the spray nozzle. The pump pressure is adjusted to spray the liquid adhesive onto the treated cellulose fibres at a predetermined rate as it exits the nozzle. An operator remotely and simultaneously turns on the insulation machine and delivery pump and applies the insulation onto a surface in a progressive sweeping and over-lapping fashion until the desired thickness or filling is achieved. Excess insulation can be removed from the surface with a commercially available insulation scrubber well known to the person skilled in the art, and recycled back into the virgin fibre stream through the use of commercially available insulation vacuuming and recycling equipment.

The present invention will be further understood from descriptions of specific examples which follow.

EXAMPLE 1

Cellulose fibre insulation in accordance with the present invention was prepared and analyzed as follows: Cellulose in Bales (Thermo-Cell 11.35 kg (25 lb) per bale Industries, Ottawa, Canada) Additive Agent Sodium Pentaborate Additive Agent Concentration 9.5% (by weight of insulation): Initial Moisture Content (dry basis): 6.8% Adhesive: 1:3 PVOH/Acetate Resin Adhesive Concentration (by weight): 7.5%

The insulation was spray-applied into simulated wall cavities measuring 240 cm×37 cm by 14 cm deep, using an insulation machine commercially available from Krendl Equipment Company.

The insulation was tested at the National Research Council (NRC) laboratories in Ottawa, Ontario, Canada.

NRC Test Results (Report # B-1156.1) @ 23+/−1° C. and 50+/−1% relative humidity Added Moisture: 9.81% Design Density: 22.9 kg/m³ (1.4 lb/ft³) Calculated Final Adhesive Content 0.85% (oven dry basis): Calculated Total Moisture 17.1% (oven dry basis):

The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto. 

1. Cellulose fibre insulation for use in wall cavities, comprising cellulose fibres and an aqueous adhesive mixture for binding the fibres at application, wherein the moisture content of the cellulose fibre insulation at application is less than 30% on an oven dry weight basis.
 2. The cellulose fibre insulation of claim 1, wherein the moisture content is 10-30% on an oven dry weight basis.
 3. The cellulose fibre insulation of claim 2, wherein the moisture content is 15-25% on an oven dry weight basis.
 4. The cellulose fibre insulation of claim 2, wherein the moisture content is less than 20% on an oven dry weight basis.
 5. The cellulose fibre insulation of claim 1, wherein the adhesive used has gelling properties and the cellulose fibres are treated with an additive which leads to a gelling of the adhesive resin on application to the cellulose fibres.
 6. The cellulose fibre insulation of claim 1, wherein the adhesive contains polyvinyl alcohol.
 7. The cellulose fibre insulation of claim 5, wherein the additive is an alkaline crosslinker.
 8. The cellulose fibre insulation of claim 7, wherein the additive is a borate having an alkaline pH in solution.
 9. The cellulose fibre insulation of claim 5, wherein the cellulose fibres are treated with a mixture of an acidic crosslinker and an alkaline compound, the mixture having an alkaline pH in solution.
 10. The cellulose fibre insulation of claim 9, wherein the alkaline compound is an alkali earth metal hydroxide, oxide, bicarbonate; carbonate or organic base.
 11. The cellulose fibre insulation of claim 8, wherein the additive is selected from the group consisting of ammonium pentaborate, ammonium tetraborate and ammonium biborate.
 12. The cellulose fibre insulation of claim 8, wherein the crosslinker is an alkali earth metal borate having an alkaline pH in solution.
 13. The cellulose fibre insulation of claim 12, wherein the alkali earth metal borate is sodium pentaborate.
 14. The cellulose fibre insulation of claim 5, wherein the concentration of the additive in the treated cellulose fibres is 1-15% (w/w).
 15. The cellulose fibre insulation of claim 13 wherein the concentration of the additive is 5-10%.
 16. The cellulose fibre insulation of claim 1, wherein the solids concentration of the aqueous adhesive mixture is 1-15% (w/w).
 17. The cellulose fibre insulation of claim 1, wherein the solids concentration of the aqueous adhesive mixture is 5-10% (w/w).
 18. The cellulose fibre insulation of claim 6, wherein the aqueous adhesive resin is a mixture comprising polyvinyl alcohol and polyvinyl acetate.
 19. The cellulose fibre insulation of claim 18, wherein the aqueous adhesive resin mixture comprises from 1 to 10 parts polyvinyl acetate to 1 part polyvinyl alcohol.
 20. The cellulose fibre insulation of claim 18, wherein the aqueous adhesive resin mixture comprises from 1 to 5 parts polyvinyl acetate to 1 part polyvinyl alcohol
 21. The cellulose fibre insulation of claim 18, wherein the aqueous adhesive resin mixture comprises 3 parts polyvinyl acetate to 1 part polyvinyl alcohol.
 22. The cellulose fibre insulation of claims 16, wherein said insulation has a final dry adhesive content of 0.25-3% (w/w).
 23. The cellulose fibre insulation of claim 22, wherein said insulation has a final dry adhesive content of 1-2% (w/w).
 24. The cellulose fibre insulation of claim 1, further comprising boric acid as a fire retardant and crosslinker.
 25. The cellulose fibre insulation of claim 1, wherein the total amount of added water is between 5 and 24%.
 26. A cellulose fibre insulation for use in wall cavities, comprising cellulose fibres and an aqueous adhesive resin for binding the fibres at application, wherein the density of the insulation is between 16.0 to 24.0 kg/m³ (1.0 and 2.0 lb/ft³).
 27. The cellulose fibre insulation of claim 24, wherein said the density of the insulation is less than 24.0 kg/m³ (1.5 lb./ft³).
 28. A method of insulating a wall surface with an aqueous adhesive-bonded cellulose material, comprising the steps of: treating cellulose fibres with an additive which causes a gelling of the adhesive upon contact, and mixing the treated cellulose fibres with the adhesive during spray application of the cellulose fibres onto the surface to form a cellulose fibre insulation on the surface, wherein the amount of aqueous adhesive in the cellulose fibre insulation is selected to achieve a moisture content in the insulation of less than 30% on an oven dry weight basis.
 29. The method of claim 26, wherein the additive is an alkaline compound.
 30. The method of claim 27, wherein the additive is an alkaline borate, rendering the pH of the adhesive alkaline upon contact with the cellulose.
 31. The method of claim 26, wherein the cellulose is further treated with an acidic crosslinker and the additive is an alkaline compound added is a sufficient amount to render the adhesive alkaline upon contact with the cellulose.
 32. The method of claim 27, wherein the alkaline compound is an alkali earth metal hydroxide, oxide, carbonate or organic base.
 33. The method of claim 28, wherein the additive is selected from the group of ammonium pentaborate, ammonium tetraborate and ammonium diborate.
 34. The method of claim 29, wherein the crosslinker is an alkaline earth metal borate.
 35. The method of claim 32, wherein the alkaline earth metal borate is sodium pentaborate.
 36. The method of claim 26, wherein the concentration of the additive in the treated cellulose fibres is 1-15% (w/w).
 37. The method of claim 34, wherein the concentration of the additive in the treated cellulose fibres is 5-10% (w/w).
 38. The method of claim 26, wherein the solids concentration of the aqueous adhesive mixture in the insulation is 1-15% (w/w).
 39. The method of claim 36, wherein the solids concentration of the aqueous adhesive mixture is 5-10% (w/w).
 40. The method of claim 26, wherein the aqueous adhesive resin is a mixture of polyvinyl alcohol and polyvinyl acetate.
 41. The method of claim 38, wherein the aqueous adhesive resin mixture comprises from 1 to 10 parts polyvinyl acetate to 1 part polyvinyl alcohol.
 42. The method of claim 38, wherein the aqueous adhesive resin mixture comprises from 1 to 5 parts polyvinyl acetate to 1 part polyvinyl alcohol.
 43. The method of claim 38, wherein the aqueous adhesive resin mixture includes 3 parts polyvinyl acetate to 1 part polyvinyl alcohol.
 44. The method of claim 26, wherein the final dry adhesive content is 0.25-3% (w/w).
 45. The method of claim 26, wherein the final dry adhesive content is 1-2% (w/w).
 46. The method of claim 26, wherein the cellulose insulation has an applied density between 16.0 to 24.0 kg/m³ (1.0 and 2.0 lb/ft³).
 47. The method of claim 44, wherein the cellulose insulation has an applied density of less than 24.0 kg/m³ (1.5 lb./ft³).
 48. The cellulose fibre insulation of claim 40, wherein the total amount of added water is between 10 and 20%. 